Breath testing system

ABSTRACT

An alcoholic breath analyzer is disclosed which responds only to alcohol content of a subject&#39;&#39;s breath. It is immune to other breath constituents, such as water and carbon dioxide, that have adversely affected certain types of prior breath analyzers and led to false test results. This immunity is achieved by a modified wheatstone bridge type alcohol detector having identical heated catalytic resistance elements in two of its adjacent legs. One breath sample, from the person being tested, is supplied directly to one of the catalytic resistance legs while another sample is simultaneously channeled, via a series-connected alcohol removal stage, to the other such leg. In this way, the two breath samples reaching the bridge are the same except for alcohol content and any effects of the non-alcohol constituents are neutralized or balanced out in the two catalytic legs. The resistance of the catalytic leg receiving the alcohol changes in response to that alcohol, thereby unbalancing the bridge and producing an output information signal the amplitude of which accurately represents the breath alcohol concentration.

Burroughs et al.

[ Dec.3, 1974 BREATH TESTING SYSTEM James A. Nowak, Glendale Heights,

' all of I11.

[73] Assignee: Borg-Warner Corporation, Chicago,

Ill.

[22] Filed: Dec. 28, 1971 [2]] Appl. No.: 213,141

[52] U.S. Cl. 23/254 E, 23/254 EF, 73/23 [51] Int, 'Cl. G01n 31/10, GOln 31/12 [58] Field of Search 23/254 E, 255 E, 232 E,

23/254 EF, 254 R, 255 R, 232 R, 232 C; 73/26, 27 R, 23

[56] References Cited UNITED STATES PATENTS 2,310,472 2/1943 Sullivan 23/255 E 3,076,697 2/1963 Miller et al 23/254 E 3,464,797 9/1969 Hagopian 23 254 R 3,558,279 1 1971 McRae et al..... 23/23212 X 3,558,283 l/l97l Freeman et al.. 23/254 E X 3,600,134 8/1971 Noller 23/254 E x Breath Breath Receiving 3 Apparatus 2 Alcohol Breath l/ I Eliminator Primary E.ramt'nerJoseph Scovronek Attorney, Agent, or Firm.lames E. Tracy [5 7] ABSTRACT An alcoholic breath analyzer is disclosed which responds only to alcohol content of a subjects breath. It is immune to other breath constituents, such as water and carbon dioxide, that have adversely affected certain types of prior breath analyzers and led to false test results. This immunity is achieved by a modified wheatstone bridge type alcohol detector having identical heated catalytic resistance elements in two of its adjacent legs. One breath sample, from the person being tested, is supplied directly to one of the catalytic resistance legs while another sample is simultaneously channeled, via a series-connected alcohol removal stage, to the other such leg. In this way, the two breath samples reaching the bridge are the same except for alcohol content and any effects of the non-alcohol constituents are neutralized or balanced out in the two catalytic legs. The resistance of the catalytic leg receiving the alcohol changes in response to that alcohol, thereby unbalancing the bridge and producing an output information signal the amplitude of which accurately represents the breath alcohol concentration.

1 Claim, 1 Drawing Figure Output Utilizing Apparatus BREATH TESTING SYSTEM BACKGROUND OF THE INVENTION Various breath testing systems have been developed for evaluating a persons breath to detect its alcohol level. In one such system, a sample of the breath to be analyzed is passed over a heated catalyst resistance element, constituting one leg of a normally-balanced wheatstone bridge, where any alcohol present in the breath sample oxidizes. The heat of this oxidation reaction causes the temperature and consequently the resistance of the catalytic element to increase, and this in turn unbalances the bridge and produces an output information signal indicating the particular alcohol level in the breath sampled.

To render the wheatstone bridge type alcohol detector immune to any deleterious effects otherwise caused by thermal conductivity, thermal changes, convection, etc. one of the legs adjacent to the catalytic leg is usually formed of a non-catalyst but otherwise identical resistance element and both of the resistance elements are simultaneously exposed to the same breath sample. With that arrangement, any change in either the catalytic or non-catalytic leg is balanced out by an equal and compensating change in the other leg. In the absence of such compensation erroneous test results would manifest. Of course, as in any wheatstone bridge current changes due to power supply variations are also cancelled out.

The operation of a conventional bridge type alcohol detector is also adversely affected by certain constituents of a persons breath, and heretofore it has not been possible to neutralize the effect of those constituents. Specifically, non-alcohol breath components, such as water'and carbon dioxide, effect changes in the resistance of one or both of the resistance elements, thereby resulting in the development of a false output signal which vdoes not accuratelyrepresent the alcohol level of the breath sampled. This undesired response of the catalytic leg to water and carbon dioxide is probably due to absorption which causes the temperature of the catalyst resistance element to increase.

The present invention constitutes a significant improvement over all prior bridge type alcohol detectors since its operation is effectively immune to breath constituents such as water and carbon dioxide and provides test results that reflect only the breath alcohol concentration. The breath testing system herein disclosed performs a considerably more accurate test than any previ ous bridge type alcohol detector.

SUMMARY OF THE INVENTION A breath testing system, constructed in accordance with the invention, comprises breath receiving apparatus for providing first and second identical samples of breath received from a subject to be tested. There is an alcohol detector which includes a normally-balanced wheatstone bridge having first and second identical heated catalyst resistance elements in respective ones of two of its adjacent legs. Means are included for supplying the first sample directly to the first catalyst resistance element. There are also means for simultaneously supplying the second sample through an alcohol removal stage to the second catalyst resistance element. The bridge unbalances in response to the presence .of alcohol in the firstsample and in so doing produces an output information signal indicative of the breath alcohol concentration. An output apparatus, such as a meter, utilizes the information signal. Any response in one of the resistance elements to a non-alcohol breath constituent will be canceled by a similar response in the other element.

DESCRIPTION OF THE DRAWING The features of the invention which are believed to be novel are set forth with particularity in the appended claims. The invention, together with further advantages and features thereof, may best be understood, however, by reference to the following description in conjunction with the accompanying drawing, the single FIG- URE of which is a diagram, partly in block form and partly in schematic, of a breath testing system constructed in accordance-with one embodiment of the invention.

DESCRIPTION OF THE ILLUSTRATED EMBODIMENT Breath receiving apparatus 10 develops, in response to breath received from a subject being tested, a pair of identical samples of that breath at respective ones of outputs 11 and 12. Apparatus 10 may take any suitable construction to facilitate the receipt of breath blown or exhaled by the subject and to deliver identical samples of that received breath to outputs l1 and 12, the unused breath being vented or dumped to the atmosphere. One example of an appropriate form for apparatus 10 is found in copending application Ser. No. 136,778, filed Apr. 23, 1971 in the names of Donald W. Collier, Joseph P. Hoppesch and Anthony C. Mamo, and issued Oct. 9, 1973 as US. Pat. No. 3,764,270. The breath receiving apparatus illustrated and described in that copending application has only one output and thus provides only one breath sample. However, it may very easily be modified to have two outputs in order to simultaneously produce the two identical sample needed in the disclosed breath taking system. A

While not essential for the proper operation of the present invention, apparatus 10 preferably includes an appropriate control device to make certain that the identical output samples constitute deep lung breath. Suitable control equipment to perform that functionis also illustrated and described in the aforementioned copending application Ser. No. l36,778. There, a breath sample is not produced at the output of the breath receiving apparatus until a continuous uninterrupted breath flow has occurred for a predetermined period, such as five seconds. A sample taken at the end of a five-second period of uninterrupted blowing or exhaling constitutes deep lung breath, from which an accurate reading of blood alcohol level may be inferred as is well known in the art.

As also shown in copending application Ser. No. 136,778 breath receiving apparatus l0 may include a series of heaters and temperature sensors to insure accurate testing under extreme conditions of use.

The alcohol concentration in the deep lung breath sampled is determined by an alcohol detector {15 which includes a normally-balanced wheatstone bridge 16 having a pair of identical heated catalyst resistance elements l7 and 18 in respective ones of two of its adjacent legs and a pair of simple, equal size resistors 21 and 22 in the other two adjacent legs. Preferably, each of elements 17, 18 constitutes a catalytic coated ceramic bead containing a resistance wire. Bridge junction 23 connects to the positive terminal 24 of a source of DC operating potential, while junction 25 is connected to the negative terminal 26 of that potential source. Direct current therefore flows from positive terminal 24 to negative terminal 26 through two parallel paths one provided by legs 17 and 18 and the other by legs 21 and 22. Since elements 17 and 18 normally have the same resistance and since resistors 21 and 22 are of equal electrical size, in the absence of any external stimulation bridge 16 will be balanced and the two junctions 28 and 29 will be established at identical voltage levels. The output of alcohol detector is derived between junctions 28 and 29 and with a zero voltage difference normally existing between those junctions no output signal will be developed by the alcohol detector.

As diagrammatically shown by channel 31 in the drawing, a breath sample emanating at output 11 is conveyed to and passes over catalytic element 17. Simultaneously, the counterpart identical sample produced at output 12 is delivered through a channel 32 to an alcohol removal stage or eliminator 33, the output of which is supplied via a channel 34 to catalytic element 18. Stage 33 may take any of a variety of appropriate forms. Preferably, it merely constitutes a heated platinum wire. Stage 33 removes only the alcohol from the sample produced at output 12 in order that element 18 will receive a breath sample identical to that received by element 17 with the sole exception of the alcohol constituent. In this way, if there is any water and carbon dioxide in the sample reaching element 17, those same constituents will contact element 18. As a result, any response of element 17 to the water and carbon dioxide will be balanced out by an equal response by element 18. Specifically, the temperature of element 17 is likely to increase (probably due to absorption) and this will cause the resistance of the. element to increase. However, element 18 will react in the same fashion as a consequence of which the resistances of elements 17 and 18 remain equal to each other, thereby maintaining the bridge in a balanced condition.

The bridge becomes unbalanced if alcohol is present in the subjects breath inasmuch as the alcohol constituent is conveyed only to catalytic element 17. The alcohol oxidizes as it passes over that element and the heat of oxidation causes the temperature and thus the resistance of element 17 to increase to an extent directly proportional to the alcohol level or concentration. Since the alcohol constituent is prevented by alcohol eliminator 33 from reaching element 18, the resistance of that element remains unchanged. With unequal resistances in legs 17 and 18, the voltage drops in those legs will be unequal as a result of which junction 28 will be established at a voltage different from that at junction 29. An output information signal is thus provided between junctions 28 and 29 for application to output utilizing apparatus 37, the amplitude or magnitude of that signal being directly proportional to and representing the breath alcohol concentration.

Output utilizing apparatus 37 may include a meter which effectively measures the information signal amplitude, thereby providing a visual display of the alcohol concentration in the tested breath sample. Alternatively, the output apparatus can be a simple bulb energized when the information signal exceeds a predetermined threshold amplitude level. Apparatus 37 may take any of a variety of different forms since there are many devices that may be controlled by an electrical signal whose amplitude signifies the alcohol level of a person's breath.

Of course, an amplifier may be interposed between alcohol detector 15 and apparatus 37 so that the information signal may be amplified before it is applied to the output utilizing apparatus. N0 amplifier is illustrated in order to simplify the drawing as much as possible.

It is to be understood that the invention may be embodied in alcohol detector bridge circuits other than wheatstone bridges. Moreover, the bridge circuit may include alcohol sensing elements other than heated catalyst resistance elements. For example, the invention may be incorporated in alcohol detectors of the ionization type or semiconductor type.

The invention provides, therefore, an improved bridge type breath analyzer which responds only to alcohol content to develop an output information signal truly representative of that alcohol content. It is effectively unresponsive to water and carbon dioxide which in the past have deleteriously affected the operation of such breath analyzers.

While a particular embodiment of the invention has been shown and described, modifications may be made, and it is intended in the appended claims to cover all such modifications as may fall within the true spirit and scope of the invention.

We claim:

1. A breath testing system for determining breath alcohol concentration, comprising:

breath receiving apparatus for providing first and second substantially identical samples of deep lung breath received from a person whose breath includes alcohol, water and carbon dioxide;

an alcohol detector including a normally-balanced,

four-legged wheatstone bridge having first and second substantially identical catalyst resistance elements in respective ones of two adjacent legs of the wheatstone bridge and a pair of equal resistors in respective ones of the other two adjacent legs of the bridge;

an alcohol removal stage including a heated platinum wire;

means for supplying said first breath sample directly to said first catalyst resistance element;

means for supplying said second breath sample through said alcohol removal stage to eliminate the alcohol content from said second sample and for then supplying the alcohol-free second sample to said second catalyst resistance element,

said first catalyst resistance element responding to the presence of alcohol in said first sample to effect unbalancing of said wheatstone bridge, an output information signal being produced by said bridge having an amplitude directly proportional to and representing the alcohol concentration of said first sample, any effect on said first catalyst resistance element from the water and carbon dioxide in said first sample being balanced by a similar effect on said second catalyst resistance element from the water and carbon dioxide in said second sample, and a meter controlled by and responsive to the amplitude of said information signal to provide a visual display of the alcohol level in the breath under test. 

1. A BREATH TESTING SYSTEM FOR DETERMINING BREATH ALCOHOL CONCENTRATION, COMPRISING: BREATH RECEIVING APPARATUS FOR PROVIDING FIRST AND SECOND SUBSTANTIALLY IDENTICAL SAMPLES OF DEEP LUNG BREATH RECEIVED FROM A PERSON WHOSE BREATH INCLUDES ALCOHOL, WATER AND CARBON DIOXIDE; AN ALCOHOL DETECTOR INCLUDING A NORMALLY-BALANCED, FOURLEGGED WHEATSTONE BRIDGE HAVING FIRST AND SECOND SUBSTANTIALLY IDENTICAL CATALYST RESISTANCE ELEMENTS IN RESPECTIVE ONES OF TWO ADJACENT LEGS OF THE WHEATSTONE BRIDGE AND A PAIR OF EQUAL RESISTORS IN RESPECTIVE ONES OF THE OTHER TWO ADJACENT LEGS OF THE BRIDGE; AN ALCOHOL REMOVAL STAGE INCLUDING A HEATED PLATINUM WIRE; MEANS FOR SUPPLYING SAID FIRST BREATH SAMPLE DIRECTLY TO SAID FIRST CATALYST RESISTANCE ELEMENT; MEANS FOR SUPPLYING SAID SECOND BREATH SAMPLE THROUGH SAID ALCOHOL REMOVAL STATE TO ELIMINATE THE ALCOHOL CONTENT FROM SAID SECOND SAMPLE AND FOR THEN SUPPLYING THE ALCOHOL-FREE SECOND SAMPLE TO SAID SECOND CATALYST RESISTANCE ELEMENT, SAID FIRST CATALYST RESISTANCE ELEMENT RESPONDING TO TH PRESENCE OF ALCOHOL IN SAID FIRST SAMPLE TO EFFECT UNBALANCING OF SAID WHEATSTONE BRIDGE, AN OUTPUT INFORMATION SIGNAL BEING PRODUCED BY SAID BRIDGE HAVING AN AMPLITUDE DIRECTLY PROPORTIONAL TO AND REPRESENTING THE ALCOHOL CONCENTRATION OF SAID FIRST SAMPLE, ANY EFFECT ON SAID FIRST CATALYST RESISTANCE ELEMENT FROM THE WATER AND CARBON DIOXIDE IN SAID FIRST SAMPLE BEING BALANCED BY A SIMILAR EFFECT ON SAID SECOND CATALYST RESISTANCE ELEMENT FROM THE WATER AND CARBON DIOXIDE IN SAID SECOND SAMPLE, AND A METER CONTROLLED BY AND RESPONSIVE TO THE AMPLITUDE OF SAID INFORMATION SIGNAL TO PROVIDE A VISUAL DISPLAY OF THE ALCOHOL LEVEL ON THE BREATH UNDER TEST. 